The recent encouraged global activities of environmental protection put strong demands for restrictions on greenhouse gases and NOx gas production. In order to reduce the total amount of such exhaust gases, practical application of fuel cell system to automobile is thought to be very useful.
Polymer electrolyte fuel cells (PEFCs) have several advantages: operative at a low temperature; high power density; and generation of water alone during power generating reaction. Among all, PEFCs using methanol as fuel are thought to be a promising power source for an electric automobile since they enables fuel supply in a liquid form like gasoline.
PEFCs are classified into two types: reformed methanol-type polymer electrolyte fuel cells which involve reforming methanol into hydrogen-containing gas using a reformer; and direct methanol polymer fuel cells (DMFCs) which utilize methanol directly without using a reformer. Practical use of direct methanol polymer fuel cells is expected due to their great advantages: weight-saving is possible since direct methanol polymer fuel cells do not require a reformer; resistance against frequent start and stop operations; significantly improved load change response; and substantially reduced catalyst poisoning.
However, several difficulties associated with implementation of DMFC have also been pointed out. For example, DMFCs use a solid-state polymer electrolyte as the electrolyte. However, when a conventional electrolyte membrane for PEFC such as Nafion™ available from Du Pont or Dow membrane available from Dow Chemical is used, it causes two major problems: methanol will permeate the membrane, and thus the membrane will be directly oxidized and electromotive power will be reduced; and there occurs melting (creeping) of the membrane at an elevated temperature, about 130° C., for increasing catalyst activity. Although no electrolyte membranes exist which can simultaneously resolve these problems, solution of these problems may greatly promote development of DMFC applicable to automatic vehicles.